This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The physiological impact of ischemia, the reduced blood flow in the heart, such as that observed during heart attacks has been of much interest to the cardiac field. Yet of all the physiological changes that occur the one least studied, or understood, is the impact of the inherent pH changes within the cells and how they might alter the native interactions between the filament proteins responsible for doing the work of the heart. Previous work in this field has examined the role of precise pH based changes in skeletal muscle and how that impacts the arrangement of these filament proteins, yet this work is nearly two decades old and never examined the impact of pH changes specifically in the cardiac system. Our goal was to examine the effects of altering the internal pH of intact paced cardiac trabeculae on the filament proteins and how that might correlate with the changes in force and calcium handling previously examined.